Fix stale path in _tc_lock_fpaths

`_tc_lock_fpaths` was written for a `test_repo.py` that lived two
directory levels deep under the repo root, at `git/test/test_repo.py`.
After the tests directory was moved up to `test/` in 0374d7c
(2020-07-12, "tests: move to root dir"; see also d5f0d48 for the
related revert that landed alongside it), `__file__` is one level
shallower, and the `../../.git/*.lock` glob pattern resolves to
`<parent-of-repo>/.git/*.lock` -- not the repository's own `.git/`.
That directory typically does not exist on CI runners or in normal
development setups, so `glob.glob(...)` has been returning `[]` and
`_rm_lock_files` has been a silent no-op for several years.

Change the relative-path miscount to match the current depth.

The previous commit added a regression test (now passing with this
change) that creates a `.lock` file in the repository's `.git/` and
asserts `_rm_lock_files()` removes it. That test fails without this
one-line correction.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: EliahKagan

test/test_repo.py

@@ -54,7 +54,7 @@ def flatten(lol):
     return list(iter_flatten(lol))
 
 
-_tc_lock_fpaths = osp.join(osp.dirname(__file__), "../../.git/*.lock")
+_tc_lock_fpaths = osp.join(osp.dirname(__file__), "../.git/*.lock")
 
 
 def _rm_lock_files():